The present disclosure relates generally to drilling systems and earth-boring drill bits for drilling a borehole for the ultimate recovery of oil, gas, and/or minerals. More particularly, the present disclosure relates to drill bits with one or more selectively engageable variable flow bores incorporated therein.
During subterranean drilling operations, an earth-boring drill bit is connected to the lower end of a drill string and is rotated by rotating the drill string from the surface, with a downhole motor, or by both. With weight-on-bit (WOB) applied, the rotating drill bit engages the formation and proceeds to form a borehole toward a target zone.
During these operations, costs are generally proportional to the length of time it takes to drill the borehole to the desired depth and location. The time required to drill the well, in turn, is greatly affected by the number of times downhole tools must be changed, added, and/or repaired during drilling operations. This is the case because each time a downhole tool is changed, added, and/or repaired, the entire string of drill pipes, which may be miles long, must be retrieved from the borehole, section-by-section. Once the drill string has been retrieved and the desired operation is complete, the drill string must be constructed section-by-section and lowered back into the borehole. This process, known as a “trip” of the drill string, requires considerable time, effort and expense. Since drilling costs are typically on the order of thousands of dollars per hour, it is desirable to reduce the number of times the drill string must be tripped to complete the borehole.
During conventional drilling operations, it is often necessary to change, replace, and/or repair the drill bit disposed at the lower end of the drill string once it has become damaged, worn out, and/or its cutting effectiveness has sufficiently decreased. Regardless of the specific motivations, each time the drill bit is changed, replaced, and/or repaired, a trip of the drill string must be performed which thus increases the overall time and costs associated with drilling the subterranean wellbore.